Generally, a land grid array (“LGA”) package comprises an integrated circuit (“IC”), a lead-frame for supporting the IC and other packages, a circuit board or card substrate secured to the lead frame, and an interconnect array between the IC and the circuit board or card. A Radio Frequency (“RF”) Monolithic Microwave Integrated Circuit (“MMIC”) is an IC for use in microwave mixing, power amplification, and low noise amplification. A flip chip is a type of MMIC mounting without using wire bonds.
The flip chip is mounted using solder beads or bumps deposited on chip pads. Typically, a bumped wafer (sliver of semi-conducting material) is cut into individual dice that are to be mounted on lead frames. The MMIC dice are then mounted face down (the chip is flipped) on the lead-frames and the solder is reflowed for bonding. An underfill process is also done where the space between the sides of the die, the first of the MMIC, and the lead-frame is filled.
As is illustrated in FIGS. 1A and 1B, conventional flip chip LGA packages 101, comprise a lead frame 103, a flip chip 111, interconnections 115, and encapsulate. 117. Current industry practice is to etch or stamp a thin piece of metal in order to create a lead frame 103. Thus, the interconnects 115 between the flip chip 111 and the circuit board or card are typically held in place via long, exposed leads to reach the center of the flip chip 111. The long leads cause energy losses, leakage, crosstalk, and inductance.
As illustrated in FIG. 2, in an effort to reduce the negative effects of the long exposed leads, ground bumps 229 on leadframe leads 203 have been incorporated into conventional lead-frame designs as a means of shielding interconnects 205. Ground bumps 229 were formed on the lead-frame leads 203 by soldering or thermocompression and situated on the sides of the RF interconnects 205. However, the size of the bumps affects performance of microwave frequencies. As may be appreciated by those skilled in the art, unless the long interconnect lead is eliminated altogether, the flip chip LGA package will continue to experience losses, inductance, leakage, and crosstalk.
Another attempt to reduce the negative effects of the long exposed leads came with a process of half-etching a front side of a lead frame substrate, molding the etched front side, and then half-etching a back side of the lead frame substrate, as shown by patent Publication No. 2006/0223240 A1. This process, however, fails to provide effective shielding, thus leaving the substrate susceptible to losses, inductance, leakage, and crosstalk.
Accordingly, it is desirable to have a method and apparatus that eliminates long leads and provides adequate interconnect shielding thereby minimizing losses, inductance, leakage, and crosstalk, and improving performance.